A lithium-ion secondary battery includes therein a positive electrode and a negative electrode which are separated by a porous separator. In production of lithium ion secondary batteries, a separator roll is used. The separator roll is obtained by winding this separator around a core having a cylindrical shape.
Patent Literature 1 discloses a separator roll having a core whose outer diameter is 5 inch or more. Patent Literature 2 discloses a separator roll having a core whose outer diameter is 200 mm and whose internal diameter of an axis-bearing section is 75 mm.